Electronic devices



y 26, 1959 J. x. SMITH 2,888,609

ELECTRONIC DEVICES Filed Oct. 19. 1953 2 Sheets-Sheet 1 8 IN VENTOR JOHN SMITH 8v 8g Ar 0 NEV United States Patent ELECTRONIC DEVICES John 1. Smith, Belmont, Mass., assignor to Raytheon Manufacturing Company, Newton, Mass., at corporation of Delaware Application October 19, 1953, Serial No. 387,015 14 Claims. (Cl. SIS-39.3)

This invention relates to improved radio frequency transmission circuits for use in electron discharge devices of the traveling wave type and to traveling wave devices using such transmission circuits.

A radio frequency transmission circuit for high power traveling wave electron discharge devices has been described in an application for United States Letters Patent of Edward C. Dench, Serial No. 382,133, filed September 24, 1953. The aforesaid transmission circuit is composed of a number of cavities made of substantially U-shaped transmission lines or loops shorted at the ends and coupled together by straps. These loops have been fabricated from round stock.

In accordance with a first embodiment of the subject invention, the shorted lines, which may be a half wave length long at the lower cutoff frequency of the network, are made with a special cross section which permits a high impedance circuit to be maintained, as in the case of the interdigital delay line, while providing the additional advantages of a more uniform direct current electric field in the interaction space, a stronger radio frequency field in the desired space harmonic, higher inductance of the strapped coupling for a given strap size, and greater uniformity in the manufacture of the circuit loops. Moreover, by making the loops hollow, the de lay network has advantages over the interdigital delay structure in that it may be adapted for fluid cooling, thereby permitting high thermal dissipation and high power capability.

A second embodiment of the subject invention involves an open wave guide loaded at the open face by a series of shorted transmission lines or loops of the type previously described, each of which is substantially one-half wave length long at the upper cutoff wave length, This loaded wave guide delay structure has been found to possess a higher impedance than that of the strapped vane anode delay line of the first embodiment, with resulting advantages in tube optics, gain and efficiency. Furthermore, assembly of the loaded wave guide structure is simpler than that of the strapped vane structure, and the structural uniformity of the loaded wave guide structure is superior to that of the strapped vane structure. This second embodiment, like the first, is amenable to fluid cooling and consequently is capable of operation at relatively high power levels.

Other and further objects and advantages of this invention will be apparent as the description thereof progresses, reference being had to the accompanying drawings, wherein:

Fig. l is a fragmentary isometric view showing a first embodiment of a periodic structure according to the invention;

Fig. 2 is a detailed view showing a modification of the strap connections shown in Fig. 1;

Fig. 3 is a cross-sectional view of the embodiment of Fig. l as modified for fluid cooling;

Fig. 4 is a fragmentary isometric view showing a second embodiment of a periodic structure;

2,888,609 Patented May 26, 1959 Fig. 5 is a cross-sectional view of the periodic structure of Fig. 4;

Fig. 6 is a detailed view of a portion of the periodic structure of Fig. 4;

Fig. 7 is a cross-sectional view of a periodic structure of the type shown in Fig. 4, as modified for fluid cooling,

Fig. 8 is a central longitudinal cross-sectional view of a traveling wave tube incorporating the first embodiment of a periodic structure;

Fig. 9 is a central longitudinal cross-sectional view of a traveling wave tube including the second embodiment of a periodic structure; and

Fig. 10 is a plan view showing the circulating system and its relation to the remainder of the periodic structure.

Referring to Fig. 1, a portion of a strapped loop periodic delay structure 10 is shown which, like that shown in the aforesaid copending application for United States Letters Patents, consists of a plurality of cavities or network sections formed by adjacent U-shaped transmission loops shorted at both ends by an electrically-conductive member and having alternate loops interconnected by a pair of metal straps.

In accordance with this invention, the cross section of the loops is made substantially triangular, as shown in Figs. 1 to 3.

The end portions 22 of each loop 12 and 12 are inserted in corresponding apertures 13 and 13' in an electrically-conductive base 11 and are secured thereto, as by brazing. Since circular apertures are readily obtainable by drilling holes in the base, the end portions of the loops are preferably machined round. It is possible, of course, to utilize triangular apertures in the base plate or, in the event that fluid cooling is not desired, to secure the ends of the loops at the surface of the base.

The first set of alternate loops are interconnected by an electrically-conductive strap 14 while a second set of alternate loops 12' are interconnected by a similar strap 14'. These straps may take the form, shown in Fig. l, in which alternately disposed projecting portions 15 and 15' may be attached to the under side of the corresponding loops, as by soldering. Alternatively, the straps may contain V-slots 17 into which the apex of the triangular loops may be inserted prior to soldering, as shown in Fig.2.

As already mentioned in the aforesaid copending application, the spacing of the straps 14 and 14' partially determines the characteristic impedance and velocity dispersion characteristics of the network, and the spacing selected will be governed by circuit design considerations.

The reasons underlying the use of transmission loops of triangular cross section will now be stated. As pointed out in the aforesaid copending application, the characteristic impedance Z, of the strapped loop delay structure is related to the characteristic impedance Z of the cavity formed by adjacent loops by a constant factor, at a given wave length.

In order to increase Z and consequently the gain of a traveling wave amplifier utilizing this network as an anode, it is necessary to increase the value of Z A high impedance is also desirable for a traveling wave oscillator. Since Z for this type of network is given by where and since a constant value of u is desirable, it is necessary to increase the value of the strap inductance L,,. For the same pitch, the average gap or distance between adjacent loops of triangular cross section is considerably greater than the average spacing in the case of loops of circular or rectangular cross section. The area of metallic surfaces of the loop near the strap in the case of triangular loops is decreased, that is, the effective length of the strap between adjacent loops is increased. As the spacing between adjacent loops is increased, the inductance of the strap interconnecting the adjacent loops is increased, for a given strap size, so that a higher impedance network may be obtained. The use of heavier straps is permitted as a result of this increase in L,,.

In this connection, the strap inductance may be further increased, as pointed out in the aforesaid copending application, by keeping the slotted portion 16 of the strap, which is bridged by alternate loops, as far from the loop as possible. The capacitance between a triangular loop and a corresponding slotted portion of a strap is less than that between a circular or rectangular loop and the same slotted portion. The inductance, which varies inversely as the capacitance, consequently increases.

A further advantage of an anode periodic structure having triangular loops is that a more uniform direct current electric field in the interaction space of a traveling wave tube utilizing the same may be obtained. With loops of triangular cross section, the composite surface of a periodic structure, formed by the several loops of the structure which is presented to the interaction space of the traveling wave tube, is substantially flat, rather than a series of rounded surfaces, as in the case of a structure using loops of circular cross section. Because the series of the loops facing the interaction space are flat, the gap between adjacent network loops at said surface (in the average gap) is considerably less than in the case of adjacent loops of circular cross section. In other words, the aforesaid composite surface of the triangular loop network more nearly approaches a solid plane substantially equidistant at all points from the cathode or sole of the traveling wave tube. Because of this comparative surface uniformity of the triangular loop structure, the direct current electric field in the interaction space is much more uniform than that obtainable when the loops of the anode periodic structure are round,

Still another advantage of the anode structure using loops of triangular cross section over previous structures using round loops is that the space harmonic content of the electromagnetic wave in the interaction space is made stronger. A Fourier analysis of the radio frequency field between adjacent network loops indicates that the amplitude of the space harmonics of the field, relative to the fundamental, at a given distance from the anode, increases as the space between said adjacent loops is decreased. Since the radio frequency electric field at the anode can exist only across the gap between network sections (loops), the decrease in spacing between adjacent network loops, brought about by the use of loops of triangular cross section, results in the production of a stronger radio frequency field in the harmonic most effective for amplification (first space harmonic), and improved interaction between the electron beam and the aforesaid harmonic propagating along the anode network.

A final advantage of loops of triangular cross section is that they may be formed readily from standard tubing of various size by means of a conventional die so that all loops are uniform and capable of receiving a fluid coolant.

In Fig. 3, the transmission loops are made hollow to permit the passage therethrough of a coolant such as water. A continuous fiuid circulating path is provided which includes a pair of headers 18 and 19 and the several ducts 20, one within each loop 12 or 12. These ducts are connected in parallel. A fluid pump (not shown) is connected to one end of each of the headers. A possible direction of fiow of the cooling fiuid is shown by arrows in Fig. 3, although the flow may be in l reverse direction as the connections to the punmp are reversed. The header, as shown in Fig. 3, consists of a U-shapcd trough which may be soldered or otherwise joined to the bottom of base 11 so as to form a fluidtight seal. The fluid cooling system shown is illustrative of one of several possible systems and the invention is not to be limited to the system shown.

When hollow loops are used instead of the solid loops of Figs. 1 and 2, the end portions of the loop are preferably of the same configuration as the remainder of the loop, and the apertures 13 in base 11 are triangular rather than circular. It is possible, however, to round off the ends of the tubular loops, as in the case of the solid loops of Figs. 1 and 2.

A traveling wave amplifier 30 is shown in Fig. 8 which incorporates the periodic structure 10 of Fig. 1. Periodic structure 10 serves as the anode of the traveling wave amplifier and comprises a base 11, which forms one of the walls of an evacuated envelope, further including an oppositely disposed wall 27, end walls 28 and 29, and a pair of side walls, not shown. Base 11 may be fastened to the contiguous walls of the envelope by soldering or by means of fastening devices such as screws.

The inner conductor 31 of a coaxial input coupling device 30 extends through an aperture 33 in Wall 11 and is attached, as by soldering, to one end 22 of the first loop at the input end of the anode structure. An output coupling device 40 is similarly attached to one end of a loop at the output end of the anode structure.

Positioned adjacent the input end of the anode 10 is a cathode structure 35 having an electron-emissive surface 36. Cathode 35 is supported by a hollow supporting cylinder 37 extending through an aperture in wall 27 of the tube envelope. Cylinder 37 surrounds a central conductor 39 which is connected to one end of a heater coil, not shown, positioned in thermal proximity to cathode-emissive surface 36.

The details of this cathode are set forth more specifically in an application for United States Letters Patent, Serial No. 255,499 of Edward C. Dench, filed November 8, 1951, now United States Letters Patent No. 2,809,328, issued October 8, 1957.

An auxiliary electrode 42 is positioned substantially parallel to the anode structure and spaced therefrom, as shown in Fig. 8. Electrode 42 which is otherwise referred to as a sole, in a U-shaped member whose bottom surface is positioned somewhat lower than the electronemissive surface 36 of the cathode. Sole 42 is supported relative to the remainder of the tube envelope by means of a pair of supporting rods 43 rigidly attached to the sole. These rods are insulatedly supported with respect to wall 27 by means of metallic members 44 sealed, in turn, to ceramic seals 45. The latter are connected to an electrically conductive cylinder 46, which surrounds rods 43, and are, in turn, attached to recesses in wall 27 surrounding the apertures through which rods 43 pass.

Positioned beyond the opposite end of sole 42, and in substantial alignment therewith, is a collector electrode 48 rigidly supported by means of a lead-in rod 49 etc tending through an aperture in wall 27 and spaced therefrom. Rod 49 is supported relative to wall 27 by means of a conductive cup 50, a ceramic cylinder 51, a metallic cylinder 52 surrounding rod 49 and sealed together like the sole supporting device previously described.

A direct current electric field may be established between the anode and the sole by connecting a source of direct current voltage, not shown, therebetween. The cathode 35 is negative with respect to the anode but may or may not be at the same potential as the sole.

A transverse magnetic field is produced in the space between the periodic anode structure and the sole in a direction normal to the electric field or in a direction perpendicular to the plane of the paper. By proper adjustment of the magnetic field, the electrons emitted from the cathode will be directed along a path adjacent the loops of the anode structure. Interaction of the electron beam with a wave traversing the anode structure will result in amplification within the traveling wave tube.

It is possible to eliminate the transverse magnetic field and to operate the traveling wave tube as a non-magnetic amplifier. In this case, the cathode-sole assembly may be replaced by a continuous cathode extending the length of the tube and similar to that described in an application for United States Letters Patent of William C. Brown, Serial No. 210,896, filed February 14, 1951, now United States Letters Patent No. 2,651,001, issued September 1, 1953.

Although the loops 12 and 12' of the anode structure shown in Fig. 8 are solid, it should be understood that tubular loops, such as shown in Fig. 3, may be used in conjunction with a fluid cooling system.

The anode structure may also be used in a traveling wave oscillator as well as in a traveling wave amplifier. In either case, the increased characteristic impedance of the network achieved by the use of loops of triangular cross section is advantageous. The tube of Fig. 8 may be altered to operate as an oscillator by removing the output connector 40 and operating with a backward space harmonic instead of with a forward harmonic.

A second embodiment of a periodic anode structure suitable for use in traveling wave tubes is shown in Figs. 4 to 6 and comprises a rectangular open wave guide 60 having a back wall 61 and two side walls 62 and 63 arranged substantially normal thereto. The three walls of the guide are preferably integral with a base portion 11 comprising a plurality of longitudinally disposed apertures 13 along opposite sides thereof. The periodic structure thus obtained is not only rugged but easily manufactored. The wave guide, however, may be separate from the base and attached thereto by soldering or the like.

Each side wall contains alternate projecting portions 65 and arcuate slotted portions 66; the slotted portions 66 of wall 62 are located opposite projecting portion 65 of wall 63 and vice versa. The projecting portions each preferably contain a centrally located V-shaped slot 68. Both rounded end portions 22 of loops 12 of Figs. 4 to 6, which are identical to those of the first embodiment shown in Figs. 1 and 2, are inserted in circular apertures 13 in the base and the loops are pressed into the V-shaped slots 68 of side walls 62 and soldered thereto, as shown in Figs. 4 to 6. The end portions of the loops are attached to the base, as by soldering, and the portion of the loops contacting the side wall projections 65 are soldered or otherwise attached thereto. The alternate loops 12' are attached to the side wall 63 of wave guide 60 at the projecting portions 65 in the same manner as loops 12.

In order to increase the inductance of the periodic structure, the spacing between each loop and the opposite side wall of the wave guide over which the loop passes is made relatively large by means of the deep slotted portion 66. The slot is shown as semicircular since this configuration is readily obtainable by machining. Any slot configuration, however, such as that shown in the straps of Figs. 1 and 2, may be used provided sufiicient clear- ,ance is obtained between the side of the wave guide and the loops.

As in the embodiment shown in Fig. 1, the loops of the loaded wave guide shown in Figs. 4 to 6 may be hollow or tubular, as shown in Fig. 7. A pair of fluid tight headers 70 and 71 are attached to the base 11 of the periodic anode structure by any appropriate means and are colinear with the ends of the loops. The cooling fluid passes along one header, through the various parallel connected loops and back through the other header.

The triangular tubular loops may be formed by drawing round or square tubing through a triangular die.

Although triangular loops are preferable to loops of other cross section, for reasons already explained, the

loaded wave guide structure may operate satisfactorily with loops of round or square cross section; in other words, the cross-sectional configuration of the loops used with the loaded wave guide structure need not be triangular.

In Fig. 9 a traveling wave oscillator is shown incorporating the periodic structure just described. The elemenets of the tube of Fig. 9 which correspond to those of Fig. 8 are indicated by the same reference numerals.

Since the tube is an oscillator, only one coaxial connector is shown. It is possible to use the periodic wave guide anode structure in a traveling wave amplifier, in which case an input and an output connector must be provided in the manner shown in Fig. 8.

The tube of Fig. 9 is shown as having a cathode and sole and, like that of Fig. 8, is adapted for use with a transverse magnetic field producing means. If an oscillator of the non-magnetic type is contemplated, the cathode and sole may be replaced by the continuous cathode previously referred to in connection with Fig. 8.

The end loop 12a of Fig. 9 is made solid and is connected to the inner conductor 31 of a coaxial connector 30. If the tube were to operate as an amplifier using both an input and an output connector, the loop 12n at the other end of the periodic structure would be made solid and would be connected to a coaxial connector, as in the case of Fig. 8. The remaining loops are tubular and, together with headers 70 and 71 mounted along the wall of the tube, as more clearly shown in Fig. 10, form a continuous path for the circulation of a cooling fluid. One end of each header is closed while the other end is connected to one of the connections of a fluid circulating pump 75.

This invention is not limited to the particular details of construction, materials and processes described, as many equivalents will suggest themselves to those skilled in the art. It is, accordingly, desired that the appended claims be given a broad interpretation commensurate with the scope of the invention within the art.

What is claimed is:

1. A periodic structure for propagating electromagnetic wave energy comprising an open wave guide having a back wall and first and second spaced side walls arranged substantially normal to said back wall and a plurality of spaced transmission elements uniformly disposed along said wave guide, alternate ones of said elements being electrically connected to opposite ones only of said side walls at points intermediate the ends of said elements.

2. A periodic structure for propagating electromagnetic wave energy comprising an open Wave guide having a back wall and first and second spaced side walls arranged normal to said back wall and a plurality of spaced tubular transmission elements uniformly disposed along said wave guide, alternate ones of said elements being electricaliy connected to opposite ones only of said side walls at points intermediate the ends of said elements, and means for effecting circulation of a cooling fluid through said elements.

3. A periodic structure for propagating electromagnetic wave energy comprising an open wave guide having a back wall and first and second spaced side walls arranged substantially normal to said back wall and a plurality of transmission elements uniformly disposed along said wave guide, alternate ones of said elements being electrically connected to opposite ones only of said side walls at points intermediate the ends of said elements, said elements having a triangular outer configuration and combining to present a surface Parallel to said back wall of said wave guide.

4. A periodic structure for propagating electromagnetic wave energy comprising an open wave guide having a back wall and first and second spaced side walls arranged substantially normal to said back wall, said side walls each having alternately disposed slotted portions and projecting portions, said projecting portions of said first side wall being located opposite said slotted portions of said second side Wall, a plurality of spaced transmission elements electrically connected alternately to said projecting portions of said side wall at points intermediate the ends of said elements.

5. A periodic structure for propagating electromagnetic wave energy comprising an open wave guide having a back wall and first and second spaced side walls arranged substantially normal to said back wall, a base portion in contact with said wave guide, and a plurality of spaced transmission elements uniformly disposed along said wave guide, alternate ones of said elements being electrically connected to opposite ones only of said side walls at points intermediate the ends of said elements, the ends of said elements being electrically connected to said base portion.

6. A periodic structure for propagating electromagnetic wave energy comprising an electrically conductive member, a plurality of spaced circuit elements of. tapered cross section connected at opposite ends thereof to opposite sides of said member and uniformly disposed along the longitudinal axis thereof, the portion of each of said elements of maximum transverse dimension combining to present a substantially continuous planar surface approximately parallel to said member, and a pair of electrically conductive straps each attached to alternate ones of said circuit elements.

7. A traveling wave electron discharge device comprising an evacuated envelope, a periodic structure mounted within said envelope for propagating electromagnetic wave energy, said periodic structure including an open wave guide having a back wall and first and second spaced side walls arranged substantially normal to said back wall, a base portion in contact with said waveguide, and a plurality of spaced transmission elements uniformly disposed along said waveguide, alternate ones of said elements being electrically connected to opposite ones only of said side walls at points intermediate the ends of said elements, the ends of said elements being electrically connected to said base portion, a source of electrons, and means for directing said electrons along a path adjacent said periodic structure and in energy interacting relationship with said wave energy.

8. A traveling wave electron discharge device comprising an evacuated envelope, a periodic structure mounted within said envelope for propagating electromagnetic wave energy, said periodic structure including an electrically conductive member, a plurality of spaced circuit elements of tapered cross section connected at opposite ends thereof to opposite ends of said member, and a pair of electrically conductive straps attached to alternate ones only of said circuit elements, the portion of each of said elements of maximum transverse dimension combining to present a substantially continuous surface parallel to said member, a source of electrons, and means for directing said electrons along a path adjacent said periodic structure and in energy interacting relationship with said wave energy.

9. A periodic structure for propagating electromagnetic wave energy comprising an open wave guide having a back wall and first and second spaced side walls arranged substantially normal to said back wall and a plurality of spaced transmission elements uniformly disposed along said wave guide, alternate ones of said elements being electrically connected to opposite ones only of said side walls at points intermediate the ends of said elements, said elements being of length greater than the distance between said side walls.

10. A periodic structure for propagating electromagnetic wave energy comprising an open wave guide having a back wall and first and second spaced side walls arranged substantially normal to said back wall and a plurality of spaced transmission elements uniformly disposed 8 along said wave guide and whose electrical length is substantially any number of half-wave lengths at the lower cutolf wave length of the structure, alternate ones of said elements being electrically connected to opposite ones only of said side walls at points intermediate the ends of said elements.

11. A traveling wave electron discharge device com prising an evacuated envelope, at periodic network mounted in said envelope for propagating electromagnetic wave energy, a principal electrode arranged coextensive with and spaced from said periodic network, said periodic network including an electrically conductive member having a principal surface and a plurality of uniformly disposed circuit elements of tapered cross section, each having at least a portion thereof attached to said member and having a major portion thereof spaced from and disposed substantially parallel to said principal surface of said member, a pair of electrically conductive straps each attached to alternate ones only of said elements adjacent said major portion of said elements, said elements cooperating with said member to form a series of network sections, the portion of each of said elements of maximum transverse dimension combining to present a substantially continuous surface approximately parallel to said principal electrode, a source of electrons, and means for directing said electrons along a path adjacent said periodic network and in energy interacting relationship with said wave energy.

12. A traveling wave electron discharge device comprising an evacuated envelope, a periodic structure mounted within said envelope for propagating electromagnetic wave energy, said periodic structure including an open wave guide having a back wall and first and second spaced side walls arranged normal to said back wall and a plurality of spaced transmission elements uniformly disposed along said wave guide, alternate ones of said elements being electrically connected to opposite ones only of said side walls at points intermediate the ends of said elements, a source of electrons, and means for directing said electrons along a path adjacent said periodic structure and in energy interacting relationship with said wave energy.

13. A traveling wave electron discharge device comprising a periodic slow wave structure for propagating electromagnetic wave energy, said structure comprising an open wave guide having a back wall and first and second spaced side walls arranged substantially normal to said back wall, a base portion in contact with said wave guide, and a plurality of spaced transmission elements uniformly disposed along said wave guide, alternate ones of said elements being electrically connected to opposite ones only of said side walls at points intermediate the ends of said elements, the ends of said elements being electrically connected to said base portion, a source of electrons, and means for directing said electrons along a path adjacent said structure in energy-exchanging relationship with said wave energy.

14. A traveling wave electron discharge device comprising an evacuated envelope, a periodic slow wave structure mounted in said envelope for propagating electromagnetic wave energy, said structure comprising an open wave guide having a back wall and first and second spaced side walls arranged substantially normal to said back wall and a plurality of spaced transmission elements uniformly disposed along said wave guide, alternate ones of said elements being electrically connected to opposite ones only of said side walls at points intermediate the ends of said elements, said elements being of length greater than the distance between said side walls, a source of electrons, and means for directing said electrons along a path adjacent said network in energy-exchanging relationship with said wave energy.

(References on following page) References Cited in the file of this patent UNITED STATES PATENTS 10 Ludi Dec. 16, 1952 Brown Mar. 23, 1954 Brown et a1. May 11, 1954 Kumpfer July 6, 1954 Pierce May 10, 1955 Hagelbarger et al May 15, 1956 Walker May 15, 1956 

